Single well vertical drive in-situ combustion process



Jan' 30 1962 J. H. HENDERSON ET AL 3,018,827

SINGLE WELL VERTICAL DRIVE IN-SITU COMBUSTION PROCESS Filed June 17. 1957 Filnited States Patent Ofilice il? Patented Jan. 30, 1962 3,013,827 SINGLE WELL VERTICAL DRIVE lN-SIT U CMBUSTION PROCESS James H. Henderson, Gibsona, and Malcolm R. J. Wyllie, Allison Park, Pa., assignors to Gulf Research it Development Company, Pittsburgh, Pa., a corporation of Delaware Filed June 17, 1957, Ser. No. 665,989 3 Claims. (Cl. 16o- 39) This invention relates to a process for the recovery of oil from oil bearing formations. It is more particularly concerned with the secondary recovery of oil by an in-situ combustion process employing a single well.

The primary recovery of oil from oil bearing formations, hereinafter referred to as pay zones, utilizes the natural pressure on the pay zone to force the oil through permeable sands to the well. The pressure on the pay zone may be sufficient to deliver oil to the well head or, if the pressure is not adequate, a suitable lift is used to raise oil from the borehole to the surface. Usually only a small fraction of the oil present in the oil bearing formation can be recovered by primary recovery processes. Secondary recovery methods in which the pay zone is repressured by the injection of gas into the upper part of the formation or water into the lower part to provide the drive required to move the oil through the formation are frequently used to increase the amount of oil recovered. In another secondary recovery process referred to as an in-situ combustion process, oil in the formation is ignited and an oxygen-containing gas is pumped into the formation at an input well to continue the burning. The oxygen-containing gas and products of combustion force oil through the pay zone to an adjacent production well from which the oil is withdrawn.

In the usual in-situ combustion process, production is hampered by the necessity of pushing a large volume of cold oil for relatively long distances through a cold formation to the production well. Often the in-situ combustion must be continued for long periods, for example several months, before the benefits of the heat liberated are realized. Because of the difficulty of controlling the rate and direction of travel of the injected oxygen-containing gases and the long time before the effects of the heat of combustion show up, the expenses incurre-d may be large. Moreover, there is a tendency for gases introduced at the injection well to rise to the top of the pay zone and by-pass a substantial part of the oil bearing formation as the gases ow to the production well.

This invention resides in an in-situ combustion process utilizing a single well in which the pay zone is fractured extensively near its top and bottom. A third fracture of small radius compared to the top and bottom fractures is made in the pay zone between the top and bottom fractures and the third fracture is sealed. An oxygencontaining gas is pumped into the top fracture and oil in the formation is ignited adjacent the top fracture whereby oil is forced from the formation into the lower fracture for delivery to the well.

The single FlGURE of the drawings is a diagrammatic illustration of a well penetrating an oil bearing formation and adapted for use in this invention.

Referring to the drawing, a well, indicated generally by reference numeral 10, is drilled through a pay zone 12 to a total depth 14. Pay zone 12 is covered by an impervious cap rock 13. Casing 16 is set through the pay zone and is cemented as indicated by reference numeral 18. The casing 16 is then perforated at 20` at an intermediate position, preferably near the middle of the pay zone, by bullets, explosives or other conventional means. The formation is fractured lightly at 22 adjacent the perforations 20 and a heat resistant cement 24 such as a high-aluminum cement is squeezed into the fracture. A suitable cement is marketed as Ciment Fondu by La Farge Aluminous Cement Company, Ltd., London, England.

The casing is next perforated at 26 just below the cap rock 13 and the pay zone 12 is extensively fractured, as indicated by reference numeral 2S, through the perforations. In order to facilitate illustration of the apparatus within the casing 16, neither the horizontal nor vertical scale is consistent through the drawings. After fracturing the upper portion of the pay zone at 28, a plug of cement, if one is left in the casing from the squeezing of cement 24 into the intermediate fracture, is drilled to about the bottom of the pay zone. The casing 16 is then perforated at 30 near the bottom of the pay zone l2 and the pay zone fractured at 32 in a manner similar to the fracture 28 at the top of the pay zone. Fractures 28 and 32 are preferably located in the upper one-fourth and lower onefourth, respectively, of the pay zone.

The well is then completed by setting a heat resistant packer 34 in the casing above the perforations Ztl. A tubing 36 is run through the packer 34 to receive production entering the casing through the bottom fracture 32. Tubing 36, which extends to the well head, is provided with suitable lifting means, for example an insert pump, not shown, for delivery of production from the well.

An ignition device 38, which may be of the type illustrated in United States Letters Patent No. 2,668,592 of J. l. Piros et al., is run in the annulus 39 between the tubing 36 and the casing 16 to a position adjacent the upper perforations 26. Ignition device 38 is supported on the lower end of tubing 40 for supplying an oxygencontaining gas. A fuel line 42 runs through tubing 40 to supply fuel which is mixed at the ignition device 38 with the oxygen-containing gas delivered through tubing 40. Tubing itl is connected at its upper end with an oxygencontaining gas supply line 44 and fuel line 42 is connected with a source of fuel through line 46. Electric energy to supply a spark at the ignition device 3S is furnished through suitable lead lines a8. A second supply line 5t) for oxygen-containing gas is connected with the annulus 39 between the casing and the tubing 36 to furnish oxygen required for the in-situ combustion process. It is preferred that the tubing 36 be insulated as shown at 52 adjacent the ignition device 38.

ln the operation of the apparatus illustrated in the drawing, a fuel, preferably gas from gas-oil separators at the lease is delivered through supply line 412 to the ignition device where it is mixed with an oxygen-containing gas delivered through tubing liti. The fuel is ignited and the combustion products pass through the perforations 26 and fracture 28 to heat the formation adjacent the fracture. During this period an excess of oxygen-containing gas is introduced either through tubing 40 or annulus 52. After the oil in the formation has become ignited, which can be determined by measurements of the formation temperature, for example, the flow of fuel through line 46 and 421 is stopped and the llow of air is continued. The air and the combustion products push the oil downwardly through the pay zone to the bottom fracture 32. Oil also flows inwardly from the pay zone surrounding the fractures, indicated by reference numeral 511i, to fracture 32. Oil flows through the fracture to tubing 36 and is then lifted to the well head.

The in-situ combustion process of this invention can be used in pay zones that have some vertical penmeability whereby the oil can ow downwardly to the bottom fracture for delivery into the well. The formation should be sufficiently consolidated that a fracture can be made from any point at the well bore and the fracture will substantially follow bedding planes in the pay zone. In such formations the top and bottom fractures will be substantially parallel and will remain substantially parallel throughout their extent. Formations of substantial thickness, for example over 15 feet thick, and particularly formations more than 20 feet thick are especially suited for use with this invention. The lower `limit of thickness of the pay zone is determined by practical considerations in making three definite, spaced fractures in the pay zone. The upper limit of formation thickness is determined only by the maximum thickness through which the oil can be forced at acceptable rates, which depends largely on the vertical permeability of the pay zone and the viscosity of the oil in the formation. The wide front over which heat is transferred to the oil, and the relatively short distance the oil travels to the bottom fracture makes the process particularly suitable for use in pay zones containing highly viscous oils.

It is preferred that the well be drilled to the bottom of the pay zone and be cased and cemented through the pay zone. The casing and surrounding sheath of cement are then perforated at the top and bottom of the pay zone and at a point intermediate the top and bottom perforations for subsequent fracturing. The top and bottom fractures are extensive and may extend for a radius of at least about 50 feet, preferably 10() to 600 feet. The maximum extent of the fracture is not limited by this invention but will depend upon the usual considerations in fracturing such as the well spacing in the field and the characteristics of the pay zone. The fracture should be propped open by a propping agent such as sand. Any of the conventional fracturing techniques, for example, the technique described in United States Letters Patent No. 2,642,142, of J. B. Clark, issued June 16, 1953, are suitable.

The intermediate fracture is very light and is merely designed to allow squeezing cement therein to extend a barrier preventing by-passing of a major portion of the formation. The intermediate fracture may extend from a minimum of about feet from the borehole to as much as one-quarter of the radius of the top and bottom fractures. The barrier formed by the cement squeezed into the intermediate fracture is important in equalizing flow downwardly through the pay zone.

Heat for ignition of oil in the pay zone can be supplied by an electric heater; however, burning a fuel in the annulus between the central tubing in the top fracture is preferred. The hot combustion gases are forced into the top fracture to heat the oil in the pay zone to a temperature at which it is ignited by air in excess of that required for burning the fuel. The ignition of the crude oil will take place along the face of the upper fracture. After ignition has been completed the injection of the oxygen-containing gas is continued to maintain the burning of oil in the formation and supply pressure which forces oil to the bottom fracture. The rate of injection will vary, depending upon the permeability of the formation and its oil content as well as the extent of the fracture. Ordinarily oxygen-containing gas will be injected into the well through the top fracture at the rate of 50,000 to 500,000 standard cubic feet per day. It is desirable that the rate of injection of the oxygen-containing gas be such that the oxygen therein is completely consumed.

In a specific example of this invention a well is drilled just through a pay zone 30 feet thick to a total depth of 2,021 feet. Seven-inch casing is set in the well and cemented completely through the pay Zone. The casing is perforated midway between the top and bottom fractures and the formation fractured for an average distance of about feet. Cement is squeezed into the intermediate fracture. The casing is then perforated near the top and bottom of the pay zone with the spacing of the perforations being feet. The formation is fractured at the top and bottom perforations for an average radius of 75 feet with a lease oil containing 1 to 2 pounds of sand per gallon.

The well is completed with tubing extending down into the well adjacent the bottom fracture through a packer between the bottom and top fracture. Natural gas at a rate of 250 standard cubic feet per hour and air at a rate of 5,000 standard cubic feet per hour are injected into the annulus above the well and ignited to heat oil adjacent to the top fracture to ignition temperature. After ignition, air injection is continued into the well and the rate increased to 500,00 standard cubic feet per day, at a pressure o-f 1,850 pounds per square inch gauge at the well head. Oil delivered through the bottom fracture is lifted through the central tubing to the well head.

The process of this invention greatly increases the recovery of oil from a well. The increased pressure in the upper portion of the pay zone resulting from the oxygen-containing gas and products of combustion aids the natural gravity drainage of oil towards the bottom fracture. By passing hot oxygen-containing gas through the portion of the pay zone from which most of the oil has been forced, much of the oil burned is oil that would ordinarily be held in the formation by capillary effects.

The very large area of the top and bottom fractures allows a large volume of gas to be injected and still maintain a very low linear velocity through the formation. Thus, a region of negligible pressure drop exists in the burned section, a high pressure gradient will exist in the region just ahead of the combustion zone and a low pressure gradient will exist through the rest of the pay which is as yet unaffected by the advancing combustion zone. Unlike the usual in-situ combustion process, the area of the combustion front remains relatively constant, thereby facilitating control of the process. The heat of combustion raises the temperature and sharply reduces the viscosity of the oil thereby further facilitating flow through the formation. Moreover residual formation pressure will force oil to flow radially into the formation between the outer perimeter of the fractures and then through thc bottom fracture to the well. The relatively high temperature of the oil in the bottom fracture reduces the viscosity of oil from the pay zone surrounding the fracture to allow that fracture to carry large quantities of oil even though the pressure differential causing flow of the oil may be small.

We claim:

1. A method of completing a well comprising drilling a well through a pay zone, setting casing through the pay zone, cementing the casing to seal it through the pay zone, perforating the casing at an intermediate position in the pay zone, forming a substantially horizontal intermediate fracture extending from the perforations into the pay zone for a radial distance of at least about 10 feet, squeezing a sealing material into the intermediate fracture and allowing the sealing material to set to form a thin, impermeable, solid barrier extending substantially horizontally into the pay zone from the well, perforating the casing near the top of the pay zone, forming a substantially horizontal top fracture near the top of the pay zone communicating with the perforations in the casing near the top of the pay Zone, said top fracture having a radius at least 4 times the radius of the intermediate fracture, propping said top fracture open with a propping agent, perforating the casing below the intermediate fracture and near the bottom of the pay zone, forming a substantially horizontal bottom fracture extending from the perforations near the bottom of the pay Zone for a radius substantially equal to the radius of the top fracture, propping said bottom fracture open with a propping agent, setting a packer in the casing between the intermediate and top fracture, running tubing through the packer, said tubing extending from the well head to a position adjacent the bottom fracture, running an ignitor into the well adjacent the top fracture, delivering an oxygen-containing gas and fuel to the ignitor to burn the fuel and ignite oil in the pay zone adjacent the top fracture, stopping the How of fuel to the ignitor, continuing the injection of an oxygen-containing gas into the top fracture to burn oil in the pay zone, and producing oil from the bottom fracture through the tubing.

2. A process utilizing a single well for the recovery of oil from a pay zone penetrated by the well comprising forming a top fracture extending substantially horizontally from the well into the pay zone near the upper boundary thereof, displacing a propping agent into the top fracture to prop it open, forming a bottom fracture extending substantially horizontally from the well into the pay zone near the bottom boundary thereof, disp-lacing a propping agent into the bottom fracture to prop it open, each of said top and bottom fractures extending from the borehole of the well radially at least about 50 feet, fracturing the pay zone between the top and bottom fractures to form an intermediate fracture having a radius between a minimum of about 10 feet and a maximum of about one-fourth of the radius of the top and bottom fractures, squeezing a cement into the intermediate fracture and allowing the cement to set therein to form a thin substantially horizontal impermeable solid barrier extending from the well radially outward into the pay zone, setting packing means in the well between the top and bottom fractures, running tubing through the packing means whereby the tubing and the wall of said well dene an annulus above the packing means communicating with the top fracture and the opening through the tubing communicates with the bottom fracture, injecting an oxygen-containing gas down the well into one of the top and bottom fractures, heating the pay zone adjacent the fracture into which the oxygen-containing gas is injected to ignite oil in the pay zone, continuing the injection of an oxygen-containing gas to burn oil in the pay zone, and delivering oil through the fracture other than the fracture into which the oxygen-containing gas is injected into the well for lifting to the well head.

3. A process as set forth in claim 2 in which the top fracture is in the upper one-fourth of the pay zone and the bottom fracture is in the bottom one-fourth of the pay zone.

References Cited in the tile of this patent UNITED STATES PATENTS Re. 23,733 Farris Nov. 10, 1953 2,368,424 Reistle Ian. 30, 1945 2,412,765 y'Buddrus et al Dec. 17, 1946 2,668,592 Piros et al. Feb. 9, 1954 2,754,911 Spearow July 17, 1956 2,767,792 Spearow Oct. 23, 1956 2,818,118 Dixon Dec. 31, 1957 2,819,761 Papham et al Ian. 14, 1958 2,851,109 Spearow Sept. 9, 1958 2,874,777 Tadema Feb. 24, 1959 

